Alternating-current control system



June 24, 1930. J. KUBLER 1,756,653

ALTERNATING CURRENT CONTROL SYSTEM Filed Feb. 3, 1927 Patented June 24, 1930 UNITED STATES PATENT OFFICE.

J'OBANNES KUBLER, OF BADEN, SWITZERLAND, ASSIGNOR TO A. G. BROWN IBOVERI & CIR, OF BADEN, SWITZERLAND, A JOINT-STOCK COMPANY OF SWITZERLAND ALTERNATING-CURRENT CONTROL SYSTEM Application filed February 3, 1927, Serial No.

My invention relates to alternating current control systems and has particular relation to a control system for supplying a load with current of variable voltage by means of a multi-tap transformer and an auxiliary boosting or depressing transformer for securing a gradual, relatively fine variation of the voltage derived from the transformer with a relatively small number of transformer taps.

Among the objects of the invention is a control system of the foregoing character in which the several parts are organized so as to require a minimum of leads and operating parts, decrease the number of arcing contact switches, avoid complicated interlocking arrangements and avoid difficulties in the insulation of the apparatus utilized in the system. 4

The novel features of my invention will be best understood from the following description of exemplifications of the invention, reference being made to the accompanying drawing wherein, Figs. 1 to 4 are diagrammatic views of the apparatus and the circuits embodying various forms of my invention; and

Fig. 5 is a chart defining the sequence of operation of the switching members in the control systems of Figs. 1 to 3.

WVhile some of the features of my invention are of broad application and may be utilized in connection with a variety of electrical systems, it has been principally developed for use in connection with railway control apparatus of the type described and illustrated in articles in the BBC Review (Mitteilungen) of 1921, pages 99 to 107 and pages 183 to 192. The foregoing articles describe the control system of the Brown Boveri Company developed for use on single phase locomotives. In order to supply the motors with currents of variable voltage, there is provided a transformer having a plurality of taps leading to points of gradually higher voltage, one end of said transformer being usually grounded. The motor may be connected to any of said taps by means of a sliding contact member. The circuit through the motor is completed 165,725, and in Switzerland March 10, 1926.

through a ground connection to the other terminal thereof. In order to prevent arcing between the sliding contact member and the transformer taps an arcing switch is connected in circuit between the motor and the sliding contact member. The arcing switch is so interlocked, either mechanically or electrically, with the sliding contact mem her as to open the circuit to the sliding contact member just before it breaks contact with the transformer tap and to close the circuit after the sliding contact member reaches the next tap.

An auxiliary sliding contact member with a serially connected arcing switch is usually also provided in order to permit change of the connections of the motor from step to step without interrupting the current flow through the motor.

In order to obtain a large number of regulating steps without unduly increasing the number of transformer taps, there is provided an auxiliary transformer so arranged as to either add or subtract a voltage component to, or from, that obtained from the taps of the main transformer. The voltage component, that may thus be introduced by the auxiliary transformer, is usually a fraction of the voltage between two regulating steps of the main transformer. For instance, if the voltage difference between two successive taps of the main transformer be 30 volts, and the voltage that may be added or subtracted by means of the auxiliary transformer be 10 volts, it will be possible to vary thevoltage supplied to the motor in steps of 10 volts each.

In the construction of such control systems, it is important to avoid, as much as possible, operations involving the interruption of lar e currents. Accordingly, the connections o the auxiliary transformer are so made as to confine the switching operations to the high voltage side of said transformer and to substantially eliminate switching operations at the low voltage side thereof. To this end, the secondary low voltage winding of the auxiliary transformer is included in the circuit "leading to the-motor and the changes in the connections required to obion While it would be possible to connect the auxiliary transformer in circuit between the 'main transformer and the ground or between the driving motor and the ground, the last two arrangements have very definite disadvantages as compared to the arrangement of the auxiliary transformer between the arcing switch and the sliding contact member. Thus, if the auxiliary transformer is connected between the main transformer and the ground, the auxiliary lOCOIIIOtl G apparatus, which is usually connected between some tap of the main transformer and the ground, is supplied by a fluctuating voltage which chan es by an amount corres 0nding to twice t e voltage of the auxiliary transformer; or if such fluctuating voltage is to be avoided, both poles of the auxiliary apparatus must be connected to the transformer, under omission of the ground connection. In the other case, wherein the auxiliary transformer is connected between the motor and the ground, the motor must be insulated against ground and will be under voltage even when the arcing switch connection to the main transformer is open. A similar condition would arise if the auxiliary transformer were connected between the arcing switch and the motor.

A- system embodying the foregoin and other features of the invention is s own, by way of example, in Fig. 1. An electric locomotive that is driven by a motor 21 is arran ed to be supplied with a hi h voltage a ternating current from a tro ey line 22 and a grounded return conductor 23. by means of a transformer. The transformer is shown to be of the auto-transformer type and com rises a serially disposed high voltage'win ing 25 and low voltage winding 26 connected between the trolley wire 22 and the ound conductor 23 respectively.

TE: grounded low voltage transformer winding 26 is provided with a plurality of,

taps 1 to fi'leading to points of gradually higher voltage. The ungrounded terminal of the motor 21 is arranged to be su plied with variable volta e from said trans ormer by means of a mam sliding switch m arran ed to slide along the taps 1 to 6 and esta lish a direct electrical connection between said taps and a main sliding bar A which is connected to the motor through an arcing switch a. The main slidin switch m is operated by a suitable contro mechanism 30, for instance, by means of a threaded spindle 31 which causes the sliding contact member to move alon the taps 1- to 6 in one direction or the ot er depending on the direction of rotation of the spindle.

The object of the arcing switch a is to avoid arcing at the contact of the sliding switch m when establishing, a contact or leaving the contact with the individual transformer taps l to 6. To this end, the arcing switch a is arranged to always open the circuit to the sliding switch m before it breaks contact with any one of the transformer taps and to close only after the sliding switch has again established contact with a transformer tap.

In the operation of locomotives, and in many other applications, it is important that the energy sup lied to the motor 21 be continuous and independent of the switch operations when increasing or decreasing the voltage supply to the motor. In the motor control system, according to my invention I secure this result with a minimum of switches, leads, and other apparatus b rovidin in addition to the main sliding switch m, an auxiliary sliding switch n arranged to he slid along the taps 1 to 6 and establish connection between an auxiliary sliding bar B and the individual taps of the transformer, like the main slidin switch. The sliding bar B is connected to e motor 21 through an arcing switch 6 which is interlocked with the auxiliary sliding switch n to positively eliminate arcing at the slidin switch contacts as explained above. switchin resistor 32 is connected between the auxi iary sliding bar B and the auxiliary arcing switch b in order to avoid short-circuiting of the individual sections of the main transformer winding 26 when the main and the auxiliary sliding switch are simultaneously connected to different transformor taps. The auxiliary sliding switch n is operated in a manner similar to the main sliding switch m by means of a spindle 33 that is driven by the control mechanism 30.

With the foregoing arrangement, and assuming that there is a direct connection between the main sliding bar A and the main arcing switch a, the voltage supplied to the motor 21 may be varied, step by step, without interrupting the current through the motor. Thus, assuming that the several switches are in the positions shown in the drawing, the motor being su plied from the transformer ta 2, and an increase of the motor voltage is desired, auxiliar sliding switch n will be moved to establis contact with tap 3; auxiliary arcing switch 6 will thereupon be closed; main ar'ing switch a will be 0 ned, main slidinggwitch m will be move into contact with the next tap 3 the main arcing switch a a in closed, an

the auxiliary arcing switch again opened.

Ananalogous sequence of operation is observed in any of the other voltage steps or when reducing the voltage.

of the transformer. To this end, I provide then be 40 volts.

an auxiliary regulating transformer 27 by means of which the voltage supplied to the motor 21 may be varied in steps corresponding to a fraction of the voltage between successive taps ofthe maintransformer 26. In accordance with the invention, the transformer 27 has a secondary winding 28 which is permanently connected in'the circuit between the main sliding switch m or main slidingbar A, respectively, and the main arcing switch a which leads to the motor. By suitably manipulating the connections of the primary winding 29 of said auxiliary transformer, I secure the effect of either short-circuiting the secondary winding 28, thus providing a direct connection between the taps of the main transformer and the motor; or adding a voltage component; or subtracting a voltage component.

To this end, I provide five auxiliary electromagnetic switches a, d, e, f, 9, whereby the various connections of the primary winding 29 of the auxiliary transformer are effected. The individual switches are shown controlled electro-magnetically through energizing lines 0 to g leading to the control apparatus 30, or in any familiar manner. By closing the auxiliary switches at and e the primary winding 29 of the auxiliary transformer may be short-circ'uited, thereby producing the effect as if the secondary winding were short-circuited, thus establishing a direct connection from the transformer tap to the motor 21 and supplying the motor with a voltage corresponding to that of the step provided by the corresponding transformer tap. By closing the auxiliary switches at and g the primary winding 29 of the auxiliary transformer is energized to induce in the secondary winding 28 a voltage that acts additively to the voltage of the transformer tap, thus increasing the voltage supplied to the motor by an amount corresponding to the voltage induced in the auxiliary transformer winding. For instance, assuming the case mentioned before with a voltage difference of 30 volts between the individual main transformer steps and a voltage of 10 volts induced in the secondary inding 28 of the auxiliary transformer. The voltage supplied to the m0- tor, when the main sliding switch m is connected to transformer tap 2 and the auxiliary switches a?) and g are energized, will On the other hand, if the auxiliary switch m be brought in a position where it establishes a connection with tap '3 of the main transformer and the auxiliary switches f and e closed, the voltage induced in the auxiliary transformer will act subtractively with respect to that derived from the tap of the main transformer. Accordingly, the voltage. su plied to the motor 21 will be 50 volts, t exceed that obtained with the immediate preceeding connection by 10 volts. The next regulating step will then be obtained by again short circuiting the primar winding 29 of the auxiliary transformer t ereby securing a direct connection of the motor 21 to tap 3 of the transformer and obtaining a voltage of 60 volts.

This system of increasing the number of regulating steps by suitably controlling the auxiliary switches a to g in the primary winding 29 of the auxiliary transformer is applied in an analogous manner in connection with the other main transformer taps, either increasing the voltage sup lied to the motor or decreasing the same. 11 order to prevent excess current flow through the primary winding 29 of the auxiliary transformer while carrying out the regulating action, auxiliary switch 0 is arranged to include, or cut out, respectively, from the energizing circuit of said primary winding 29 an auxiliary switching resistance 35. This auxiliary resistance is always included in the circuit of the transformer winding 29 before the switches d to are manipulated to effect a change in the transformer connec tions; and is cut out or short-circuited after the new transformer connection has been established.

In the preferred embodiment of the invention, the operation of the individual switches 0 to g is suitably controlled from the control apparatus 30 so as to secure the most desirable and effective sequence of operations when carrying .out the regulating action, the operation of the various switches being suitably synchronized as is well known in the art. For instance, the several switches may be operated in accordance with the sequence chart, Fig. 5. The first line of the chart designates the individual switches a to g of the control system shown in Fig. 1 and the various positions that the main sliding switch m and the auxiliary sliding switch n will assume when going through a full regulating step of the main transformer, namely from tap 2 to tap 3 thereof. The index'used in connection with the characters m and n designating the main and auxiliary sliding switches respectively, indicate the relative positions of the two switches. Thus m indicates that the sliding switch 9124 makes contact with tap 2 of the main transformer; m indicates that sliding switch m is in the position between taps- 2 and 3 and is not in contact with any of said taps, et cetera.

The characters w in the columns below characters designating the several switches at is, it will vidual lines of the c and switch positions indicate that the respective switch is closed or that the sliding switch is in the position indicated by the respective column. Bgnfollowing the indiart, C1 to C13, the

sequence of the connections will readily be obtained. s 9

By following the system of re lation explained hereinabove, it is possi lev thus to onl two.

y connecting the regulating transformer between the sliding switch and the arcing switch, one terminal of the motor may be pzrmanently grounded and the motor will rendered dead whenever the arcing switches are open. With this connection the auxiliary aplparatus may be supplied with a substantia 1y constant voltage independent of the voltage sup lied to the motor by connecting sald auxi iary ap aratus between the ground and a tap o the main transformer.

In the foregoing arrangement the voltage supplied to the rimary winding 29 of the auxlliar trans ormer is derived from a point 0 the main transformer at the junction betwen the high voltage windings 25 and the low voltage windings 26. Accordingly, the voltage supplied to the auxiliary transformer will be constant and the volt-age induced in the secondary winding 28 of said transformer will likewise be constant. In many cases it is desirable to vary the voltage that may be induced by means of the auxiliary boosting or depressing transformer 27. One feature of my invention resides in an arrangement permitting such variation of the voltage induced in the auxiliary regulating transformer 27 without the use of special tappings or switch means.

7 According to the invention, the primary winding 29 of the auxiliary transformer is so connected that the voltage supplied thereto varies by reason of the variation of the voltage supplied to the motor 21. As shown in Fig. 2, secure this effect by arranging the connections of the auxiliary transformer in such manner that one end thereof is connected to a oint on the main transformer winding an the other end thereof is connected to the main regulating switch. In the embodiment of Fig. 2, the primary winding 29 of the auxiliary transformer is ar ranged to be connected with one end to the ground and with the other end to the motor side of the arcing switches a and I).

Since the voltage impressed upon the motor varies from step to step with the position of the main regulating switches, the voltage applied to the primary of the auxiliary transformer will also vary;

If the primary voltage and the ratio of auxiliary transformer is chosen to give a prima voltage equal to about one-third of the v0 tage difference between the first two taps 1 and 2 of the main transformer, and if the taps 2 to 6 of the main transformer are disposed at gradually increasing distances, the voltage steps secured with the auxiliary transformer and the connections as shown in Fig. 2 will likewise gradually increase corresponding to the increase of the voltage in the steps of the main transformer.

'In Fig. 3 I have shown a modification of the invention in which the voltage supplied to the auxiliary transformer is the sum of a constant component, and of a variable component, the latter varying with the voltage impressed upon the motor 21. To this end I provide the main transformer with a supplementary winding 41 which is connected between the ground and one terminal of the primary winding 29 of the auxiliary transformer 27, the other terminal of the auxiliary transformer being arranged to be connected to the tapping switch of the main transformer winding, for instance, by connecting it to the motor terminal of the arcing switches as in the arrangement of Fig. 2.

The modification of the invention shown in Fig. 4 is similar to that of Fig. 2 except that the boosting transformer is connected between the arcin switches and the motor. Many other modi cations will suggest themselves to those skilled in the art and I desire that all such modifications be embraced within the scope of the claims appendedhereto.

I claim as my invention:

1. In an alternating current control system comprising a transformer having a plurality of taps for deriving therefrom a plurality of increasing voltages, a load having one terminal permanently connected to said transformer and means for connecting the other terminal of said load to the taps of said transformer, said means comprising switch means for establishing successive connections with the taps of said transformer and an arcing switch connected between said switch means and said load, means for va ing the voltage impressed u on said load in steps smaller than the steps etween the taps of said main transformer, said means comprising an auxiliary transformer having a nected to said arcing switch for varying the voltage impressed on said auxiliary transformer in accordance with the variation of the voltage derived by said switch means.

5. An arrangement according to claim 1, characterized by a supplementary transformer winding operable to provide a supply -for the primary winding of said auxlliary transformer variable in amount proportional to the load voltage.

6. In a control system of the character described, a supply transformer winding having voltage taps, switch means operable to provide selective connection with said taps, a motor having one side thereof normally grounded, second switch means connected to the other side of said motor, a second transformer having a secondary winding providing an operating connection between said first and second-named switch means, said second transformer having a primary winding, and means for controlling current flow in said primary winding.

7. In a control system of the character deing voltage taps, switch means operable to provide selective connection with said taps, a motor having one side thereof normally grounded, second switch means connected to the other side of said motor, a second transformer having a secondary winding providing an operating connection between said first and second-named switch means, said second transformer having a primary winding, means providing for voltage supply to said primar winding variable in amount proportional y to the V0 lt& e across said motor, and means for contpo ling current-fiow in said primary winding.

In testimony whereof I have hereunto subscribed my name this 19 day of January A. D. 1927, at Zurich, Switzerland.

J OHAN NES KUBLER.

scribed, a supply transformer winding hav- 

